Ask him how he likes it played with. As an uncut man, we like to show off
For playing with the glans covered: sliding your tongue under it feels amazing, although that can be tricky if his skin is tight and fits snugly against the glans when erect, although a wet tongue should not have much trouble getting in there. Slurping on the skin while the tongue slides in is a good trick to get in there. If you're good at maneuvering your tongue, swirling it around the glans while you're under the skin is a move that will drive him crazy.
As for retracting it, hold the skin over covered glans it and slide it down as far as it will go naturally without forcing it. Again, this will depend on how tight he is and on how long/loose his frenulum is as well. For some guys, we can retract it all the way, fully exposing the glans and we might even be able to pull it tightly all the way back and look 'cut'. For others with a tighter opening, that might be a little painful and they are more comfortable retracting it partially down the glans or only right after the glans pops out.
Also, if you're wanking him off, just know what we don't need as much force or friction as cut guys do. I've had to learn this by telling my cut bf to go easier on me. Try not to wank a dry glans too much. His precum or lube is your friend. Spit to a lesser degree as it dries out fast.
In all fairness, if he's uncomfortable or in pain he will/should let you know. As someone above said, just let him know you've never played with an intact cock before and you're curious to try it out. If he's a decent guy, he should be more than glad to instruct you.